A new Release 8 work item has been created in 3GPP standardization fora in order to enhance the performance of the RACH (Random Access Channel) transport channel for the UMTS (Universal Mobile Telecommunications System) FDD (Frequency Division Duplex) mode based on W-CDMA (Wideband Code Division Multiple Access). Objective of the work item is to enhance the RACH in terms of capacity, throughput and transmission delay. To achieve the goals the following techniques are considered: the E-DCH (Enhanced Dedicated Channel) transport channel is used in the RRC (Radio Resource Control) state CELL_FACH as common resource, support of 2 ms and 10 ms TTIs (Transmission Time Intervals), closed-loop power control, NodeB scheduling and HARQ (Hybrid Automatic Repeat Request). In each mobile radio cell up to 32 common E-DCH resources can be configured which are broadcast to all UEs (User Equipments) in a mobile radio cell.
As mentioned the E-DCH transport channel is subject to NodeB scheduling, i.e. NodeB controls the E-DCH radio resource of a UE. In more detail, NodeB transmits in downlink so-called scheduling grants which indicate to the UE the maximum allowed E-DPDCH (E-DCH Dedicated Physical Data Channel)/DPCCH (Dedicated Physical Control Channel) power ratio.
Two types of scheduling grants are specified:
i) Absolute Grants are sent on the E-AGCH (E-DCH Absolute Grant Channel) physical channel which provide an absolute limitation of the maximum allowed E-DPDCH/DPCCH power ratio the UE may use;
ii) Relative Grants are sent on the E-RGCH (E-DCH Relative Grant Channel) physical channel which provide a relative limitation of the maximum allowed E-DPDCH/DPCCH power ratio the UE may use.
The current working assumption regarding NodeB scheduling is that the UE has to monitor the E-AGCH physical channel every TTI (i.e. 2 ms or 10 ms). But this results in a high UE battery consumption.